Feeding in Turtles: Understanding Terrestrial and Aquatic Feeding in a Diverse but Monophyletic Group

Abstract

Turtles are one of the oldest known sauropsid orders that appeared about 240 million years ago. Within the vertebrates, they have evolved the most unusual body plan, with most of their body inside a protective box made of bone and keratin. This peculiar morphology has persisted since the late Triassic, but has allowed them to adapt to very diverse habitats, ranging from marine and freshwater to purely terrestrial environments, from temperate to tropical regions of all continents except Antarctica. The majority of turtles are carnivorous, but they can shift to omnivorous and herbivorous diets during ontogeny. With respect to their feeding biomechanics, many turtle species use simple jaw prehension. Nevertheless, some aquatic species have developed specializations for suction feeding, and terrestrial species utilize tongue-dependent food uptake and transport. As might be expected, the morphology of the turtle feeding apparatus is closely associated with feeding habitat. Aquatic species have flat skulls, a large ossified hyobranchial apparatus with a small tongue, whereas purely terrestrial species possess the opposite: a high skull, and a small cartilaginous hyolingual apparatus with a large muscular and movable tongue that allows active lingual transport of food objects from the environment to the esophagus. Since turtles are characterized by a very long evolutionary history within diverse habitats, they are one of the most suitable groups within vertebrates to present morphological and behavioral variations and adaptations related to feeding medium and food type.